Rockwell Automation FactoryTalk Transaction Manager User Guide - Manual (Page 102)

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FactoryTalk Transaction Manager User Guide
102
Setting the transaction scan rate for a scheduled transaction lower than the
transaction timeout may cause the second transaction to fail because only one
scheduled transaction can run at a time.
Transaction Completion
It is important to determine when the Transaction Control Manager service
or FactoryTalk Transaction Manager service considers a transaction to be
complete because the Transaction Control Manager service or FactoryTalk
Transaction Manager service only runs one occurrence of a scheduled
transaction at a time. The next occurrence cannot start until the current
transaction is complete. Also, if a transaction has a Transaction Result
Binding, the Transaction Result is written when the transaction completes.
Cached Transactions
If you select Use Cache Transaction Files from the Transaction Definition
dialog box, unidirectional transactions complete as soon as the data is
written to the cache file. The data is not yet stored to the database, but is on
the disk.
Real-time Transactions
If you select Real Time Storage from the Transaction Definition dialog box,
unidirectional transactions complete when the Transaction Control Manager
service or FactoryTalk Transaction Manager service receives a reply from
the enterprise connector that the data has been stored. This means that the
time necessary for the enterprise system to store the values is included in the
transaction completion time. This may cause the transaction to timeout if the
Transaction Control Manager service or FactoryTalk Transaction Manager
service has not received the reply from the enterprise connector in the
allotted time. The transaction timeout does not determine if the data was
logged to the database; the transaction can time out prior to sending the data
to the database or after the data was successfully stored.
The table below shows how FactoryTalk Transaction Manager handles each
transaction type and storage method.